The role of ion translocations in the transduction of the hormonal message in the plasma membrane will be studied in the human platelet. The membrane potential of the platelet will be determined with the membrane potential sensitive lipophilic cation, triphenylmethylphosphonium ion. Specific ion transport and its role in transduction will be evaluated with ionophores and ion transport inhibitors as well as the use of impermeant ions. The biological response, platelet aggregation will be evaluated by the aggregating agents adenosine diphosphate, thrombin and catecholamines. The role of membrane potential and specific ions on the aggregation response to these ligands will be evaluated. In addition, the binding to the catecholamine receptor as influenced by ions and membrane potential will also be studied.